The use of solid state crystal counters for measuring intensities or doses of gamma radiation offers numerous advantages over Geiger-Mueller counters. However the solid state counters present problems if used in an environment with both fast neutrons and gamma rays as in the vicinity of nuclear explosions. This disadvantage has made solid state counter unacceptable for use in Army tactical surveillance equipment and in other applications where performance of radiation detectors must not be impaired by certain doses of fast neutrons. It has been suggested that these solid state counters can be hardened to reduce the effects of these fast neutrons, however this cannot completely eliminate the problem.
The present invention comprises a novel circuit which produces accurate readings of both radiation doses and dose rates regardless of degradation of the performance of solid state crystal counters caused by fast neutron exposure. The circuit adjusts itself automatically to compensate for the varying charge collection efficiency of the crystal detector caused by the fast neutrons, to yield a constant measured count rate for a given dose rate of incident gamma radiation.